1. Field of Invention
The present invention relates generally to the field of railroad couplers, and more specifically to American Association of Railroads (“AAR”) Standard E and F type railroad car couplers, especially to the knuckles used in these couplers. More particularly, the invention relates to a lightweight knuckle that is suitably strong while also still allowing the knuckle to be the weak point of the coupler. In addition the invention relates to reducing the weight of the knuckle while maintaining and/or improving the fatigue resistance of the knuckle.
2. Brief Description of the Related Art
Railcar couplers are disposed at each end of a railway car to enable joining one end of such railway car to an adjacently disposed end of another railway car. The engageable portions of each of these couplers are known in the railway art as a knuckle. For example, railway freight car coupler knuckles are disclosed in numerous U.S. patents, such as, for example, including in the following U.S. patent documents: U.S. Pat. Nos. 461,312; 533,985; 693,998; 2,689,051; 4,024,958; 4,206,849; 4,605,133; 5,582,307 and U.S. patent application no. 2009/0289024. In addition, lightweight railway freight car coupler knuckles are disclosed in U.S. Pat. Nos. 5,954,212 and 6,129,227.
Coupler knuckles are generally manufactured from cast steel weighing approximately 84 lbs. The cast steel used is grade E, tensile strength 120,000 psi, yield strength of 100,000 psi, elongation of 14%, reduction of area 30%. These knuckles fatigue crack over time which eventually leads to knuckle failure.
Knuckle failure accounts for about 100,000 train separations a year, or about 275 separations per day. Most of these separations occur when the train is out of a maintenance area. In such cases, a replacement knuckle, which can weigh about 80 pounds, must be carried from the locomotive at least some of the length of the train, which may be up to 25, 50 or even 100 railroad cars in length. The repair of a failed coupler knuckle can be labor intensive, can sometimes take place in very inclement weather, can cause train delays and is a two-man job because of the suggested 50 lbs per person lifting limits.
The front core of a knuckle is commonly referred to as the finger core. The finger core is commonly constructed to produce an internal cavity having thin ribs. These ribs made out of the standard grade E cast steel have demonstrated a weakness to the load environment with the development of fatigue and/or hot tear cracks. The fatigue cracks can grow over time and eventually lead to knuckle failure which results in separation of railcars. Separately, internal or external cracks in the knuckle are a cause for replacement of the knuckle.
The rear core of a knuckle is commonly referred to as the kidney core. Knuckles can sometimes break within this portion of the knuckle and this has proven to be a very undesirable location for a failure. A failure in this region of the knuckle can lead to knuckle jamming within the coupler body and prevent a change out of a failed knuckle, thereby requiring the entire coupler assembly to be replaced, a very costly repair.
There is a need for a knuckle with improved strength or fatigue life while still allowing it to be the weak link in the coupler system and fail under high loading conditions.
Further, there is a need for a lighter weight knuckle with similar strength or fatigue life while still allowing it to be the weak link in the coupler system and fail under high loading conditions.
In addition, there is a need for a lightweight knuckle, under 50 lbs, with strength or fatigue life similar to knuckles weighing more than 50 lbs, while still allowing the lightweight knuckle to be the weak link in the coupler system and fail under high loading conditions.
Additionally, there is a need for a lightweight knuckle, under 50 lbs, with improved fatigue life and similar strength to knuckles weighing more than 50 lbs while still allowing it to be the weak link in the coupler system and fail under high loading conditions.